Wavelength division multiplexing (WDM) is put into practical use as one of technologies to realize bulk data transmission in optical communication systems. Multiple channels having different wavelengths are provided in the WDM. In other words, multiple optical signals having different wavelengths are multiplexed in a WDM signal.
Optical add-drop multiplexing (OADM) apparatuses are provided in nodes of WDM transmission systems that transmit WDM signals. The optical add-drop multiplexing apparatuses are capable of splitting optical signals having specified wavelengths from the WDM signals to lead the optical signals to clients. In addition, the optical add-drop multiplexing apparatuses are capable of inserting client signals having arbitrary wavelengths into the WDM signals. Furthermore, many optical add-drop multiplexing apparatuses include optical channel monitors (OCMs) for monitoring wavelength channels of the WDM signals.
FIG. 1 illustrates an example of the configuration of optical add-drop multiplexing apparatuses each including optical channel monitors. Two optical add-drop multiplexing apparatuses 100A and 100B provided on optical transmission lines are illustrated in FIG. 1. The optical add-drop multiplexing apparatuses 100A and 100B are hereinafter collectively referred to as an optical add-drop multiplexing apparatus 100.
The optical add-drop multiplexing apparatus 100 includes an OADM device 101, an optical beam splitter (BS) 102, an optical amplifier 103, an optical multiplexer 104, an optical channel monitor (OCM) 105, a controller 106, an optical demultiplexer 107, an optical amplifier 108, an optical beam splitter (BS) 109, an optical channel monitor (OCM) 110, a controller 111, a monitoring signal transmitter 112, and a monitoring signal receiver 113. The configuration and the operation of the optical add-drop multiplexing apparatus 100A are substantially the same as those of the optical add-drop multiplexing apparatus 100B. The operation of the optical add-drop multiplexing apparatus 100A will now be described.
The OADM device 101 may insert a client signal into a WDM signal. In addition, the OADM device 101 adjusts the power of each channel of the WDM signal in accordance with an instruction from the controller 106. The OADM device 101 includes a wavelength selective switch (WSS).
The optical beam splitter 102 splits the WDM signal supplied from the OADM device 101 to lead the WDM signal to the optical amplifier 103 and the optical channel monitor 105. The WDM signal output from the OADM device 101 in the optical add-drop multiplexing apparatus 100A is transmitted to the optical add-drop multiplexing apparatus 100B.
The optical channel monitor 105 monitors the power of each channel of the WDM signal supplied from the OADM device 101. The optical amplifier 103 amplifies the WDM signal supplied from the OADM device 101. The optical multiplexer 104 multiplexes a monitoring signal supplied from the monitoring signal transmitter 112 on the WDM signal amplified by the optical amplifier 103.
Accordingly, the WDM signal and the monitoring signal are transmitted from the optical add-drop multiplexing apparatus 100A to the optical add-drop multiplexing apparatus 100B through an optical transmission line 120A. Similarly, the WDM signal and the monitoring signal are transmitted from the optical add-drop multiplexing apparatus 100B to the optical add-drop multiplexing apparatus 100A through an optical transmission line 120B.
The optical add-drop multiplexing apparatus 100A receives the WDM signal and the monitoring signal transmitted from the optical add-drop multiplexing apparatus 100B. The optical demultiplexer 107 in the optical add-drop multiplexing apparatus 100A leads the WDM signal that is demultiplexed to the optical amplifier 108 and leads the monitoring signal that is demultiplexed to the monitoring signal receiver 113. The optical amplifier 108 amplifies the WDM signal. The optical beam splitter 109 splits the WDM signal amplified by the optical amplifier 108 to lead the WDM signal to the optical channel monitor 110. An optical splitter 115 splits the WDM signal output from the optical beam splitter 109. A specified wavelength is selected from the WDM signal that is split and the WDM signal having the selected wavelength is transmitted to a client.
The optical channel monitor 110 monitors the power of each channel of the WDM signal received from the optical add-drop multiplexing apparatus 1006. The controller 111 generates a monitoring signal including control information to be transmitted to the optical add-drop multiplexing apparatus 100B on the basis of the result of the monitoring by the optical channel monitor 110. The monitoring signal transmitter 112 leads the monitoring signal generated by the controller 111 to the optical multiplexer 104.
The monitoring signal receiver 113 in the optical add-drop multiplexing apparatus 100A receives a monitoring signal transmitted from the optical add-drop multiplexing apparatus 1006. The controller 106 controls the OADM device 101 on the basis of the result of the monitoring by the optical channel monitor 105 and the monitoring signal received from the optical add-drop multiplexing apparatus 1006. Specifically, the controller 106 controls the OADM device 101 so as to compensate or suppress the power deviation between the channels of the WDM signal.
As described above, the optical add-drop multiplexing apparatus 100A adjusts the power of each channel of the WDM signal to be transmitted to the optical add-drop multiplexing apparatus 100B on the basis of the power of each channel of the WDM signal to be transmitted to the optical add-drop multiplexing apparatus 100B and the monitoring signal received from the optical add-drop multiplexing apparatus 1006. In addition, the optical add-drop multiplexing apparatus 100A monitors the power of each channel of the WDM signal received from the optical add-drop multiplexing apparatus 100B and notifies the optical add-drop multiplexing apparatus 100B of the result of the monitoring by using the monitoring signal.
Signal light monitors that monitor the power of each signal light of wavelength division multiplexing signal light are proposed as a related technology. Such a signal light monitor includes an optical splitter provided on an optical fiber transmission line; a wavelength tunable filter that transmits a light component having a specified wavelength included in the light split by the optical splitter; a sweeper that sweeps the wavelength transmitted through the wavelength tunable filter in a specified wavelength region; a photo detector that receives the light transmitted through the wavelength tunable filter; a sampling unit that samples the output from the photo detector; a storage unit that stores the variation in time in the sampling unit; and an arithmetic processor that performs arithmetic processing to the wavelength output from the photo detector on the basis of data stored in the storage unit. For example, such a technology is disclosed in Japanese Laid-open Patent Publication No. 10-173266. An optical multiplexer/demultiplexer described in Japanese Laid-open Patent Publication No. 2006-310963 is known as another related technology.